Abstract Substance use disorders (SUDs) continue to be one of the most serious public health problems in the US.1 Studies have consistently documented a substantially higher prevalence of SUDs among adults under criminal justice supervision in the community (i.e., probation or parole) as compared to the general population.2-4 There is growing recognition that addiction is a chronic health condition, and individuals with SUDs typically cycle through multiple periods of treatment, abstinence, and relapse over several years to achieve and maintain recovery.5 Studies show that continuing care interventions can provide ongoing support or extend primary treatment gains with respect to reducing substance use, relapse, and criminal activity.12, 6-12 Recent diffusion of Internet and smartphone technologies among disadvantaged populations13,14 now offers unprecedented opportunities for increasing access to quality continuing care interventions as well as chronic disease self- management tools. Probationers and parolees at high risk for drug abuse relapse and involvement in health compromising behaviors are an important population that stands to benefit from continuing care technologies. However, to date, no such technologies exist that are specifically tailored to meet the unique needs of this high-risk population. Building on our team?s extensive experience in the fields of criminology and substance use, we propose to complete the development of a Continuing Care mobile application (app) and conduct a randomized controlled trial to assess efficacy among clients on probation or parole who are enrolled in outpatient substance use treatment. The app is designed to meet the recovery and personal support needs of probationers and parolees with SUDs who are at elevated risk of relapse, re-arrest, and incarceration. It is guided by the principles of the transtheoretical model of behavior change and app content is derived from the Your Own Reintegration System (YOURS) program,15 an empirically-supported16 intervention that focuses on substance use recovery, reducing criminal thinking and behavior, and managing and building support systems. If proven to be efficacious, the app could be deployed across the national network of outpatient treatment providers, and be highly significant in its direct impact on public health.